| A study of coupling in superlattices of lead and silver nanoparticles, or quantum dots (QDs) is presented. Coupling interactions between QDs were varied systematically through chemical control over particle size, ligand, and disorder. A novel synthesis of superconducting lead QDs with 10% size distribution and average size of 20 nm was developed. Interparticle separation distances were varied from approximately 26 to 11 Å by varying the passivating organic ligand. Isolated particles were too small to exhibit a Meissner effect by themselves, and so it was possible to employ SQUID magnetometry as a zero-background probe for Cooper pair delocalization in these solids. As the interparticle separation distance was decreased, the quantum dot solids progressed from a Mott insulator to a strongly localized superfluid, and finally to a weakly localized superfluid.; The role of disorder in exchange coupled silver QD monolayers was probed by Surface Potential (SP) microscopy. SP images were reported for 2D arrays of Ag QDs subjected to a voltage gradient. The microscopic structure of spatial patterns of the surface potential varied systematically as the packing and/or size distribution disorder was changed. These patterns appear as either islands or stripes for disordered systems, and then coalesce for the case of compressed, ordered arrays. These features are in close correspondence with quantum mechanical computations, thereby allowing for a systematic interpretation of the observations in terms of the electronic Hamiltonian array. |
